The invention relates to flat panel displays, and more particularly to illumination for such flat panel displays.
Flat panel displays are widely used in applications where the depth dimension of a cathode ray tube is determined to be excessive. A variety of flat panel display technologies have emerged each having unique advantages. Plasma panel, electrochromism, colloidal suspension, gas discharge and liquid crystallinity are but some of the emissive and non-emissive technologies used by flat panel display manufacturers. Non-emmissive flat panel displays, such as liquid crystal displays (LCDs) require a light source especially in low light or night usage. One such application that is becoming increasingly common is aircraft cockpit displays for avionics equipment. Although not constrained to avionic LCD applications the present invention will be described in terms of such usage. It is understood that the teachings of the present invention are not limited to avionic LCD applications but may be utilized by any flat panel display using backlighting.
The principle of operation of LCD's is well known in the art but for purposes of understanding the background of the present invention, it can be stated that LCD's operate by reducing the transmissibility of light through a thin layer of a liquid crystalline material when an electric field is applied. Since the effect is localized, shapes and characters can be drawn on an LCD by carefully controlling the application of the electric field. Unlike cathode ray tubes which LCD's are replacing, LCD's are not self-illuminating. Therefore, some sort of backlighting is required in order for LCD's to be viewed.
Backlighting is conventionally accomplished by locating a fluorescent lamp device in a sealed cavity directly behind the LCD. The fluorescent lamp is generally comprised of an elongated bulb which may be "U", "N" or "M" shaped, as known in the prior art. The shape of the light source bears direct impact upon the light intensity across the LCD and just as importantly, inherent "dark spots" or areas of lower light intensity. Typically dark spots occur in close proximity to open locations in any given lighting configuration. For example, the top portion of the "U", formed by the gap between the upright members, would be an inherent dark spot in applications using such a U shaped bulb.
Accordingly, an apparatus for illuminating LCD applications of uniform or near uniform intensity across the entire viewing panel would be a significant improvement for such applications. The present invention discloses a variety of embodiments of such apparatus.